Centralized HIV-1 immunogen approach is an important strategy to explore for preclinical testing to overcome HIV- diversity. For induction of neutralizing antibodies, centralized genes should capture the conserved Env regions that are important for virus infectivity. We have recently shown in initial proof of concept studies for use of consensus Envs for immunogen design, that year 1999 CON6 gp120 and gp140 Env proteins expressed wildtype Env neutralizing epitopes, and were able to induce antibodies that neutralized about 30% of wild-type HIV-1 primary isolates. The second proof of concept milestone needed for a firm rationale for the work proposed in Project 2 has also been achieved within the last year?that of demonstration of iterative improvement of consensus gene induction of neutralizing antibodies, with year 2001 anti-CON-S gp140CFI antibodies shown to neutralize the same spectrum of B isolates as CONG gp140, and, in addition, shown to neutralize a significant subset of non-B HIV-1 primary isolates. Project 2 will synergize with Projects 1, 3 and 4 and Cores B and C by exploring ways to further enhance the immunogenicity of centralized HIV-1 genes and proteins for their ability to induce more broadly reactive neutralizing anti-HIV-1 antibodies. Specific Aim 1. To determine the immunogenicity of newer group M consensus and subtype consensus Envs compared to Year 2001 group M consensus Env, CON-S. Specific Aim 2. To enhance the immunogenicity of Year 2001 CON-S Env for induction of neutralizing antibodies. Specific Aim 3. To determine the antigenicity and immunogenicity of newly designed centralized Envs from Project 1 and Core B.